Determination of stresses and movements



SepLB, 1925. 1,552,443 I H. F. ROACH DETERMINATION OF STRESSES AND MOVEMENTS Filed Nov. 1 2. 1921 2 Shets-Sheet 2 /4 5 v l /9 l8 Patented Sept. 8, 1925.

UNITED STATES HARRY F. Boner-r, OF ST. LOUIS, MISSOURI.

DETERMINATION OF STRESSES AND MOVEMENTS Application filed November 12, 1921. Serial No. 514,522.

To all whom it may concern:

Be it known that I, IIARRY F. RoAoH, a citizen of the United States, residing in the city of St. Louis and State of Missouri,have invented new and useful Improvements in the Determination of Stresses and Movements, of which the following is a specification.

This invention relates to a process for determining the maximum stress in the fibres of a member which is subjected to a load; and for investigating the effect of wheel loads and track reactions. While the invention may be employed to determine stresses in practically any structure in which a substantial distortion occurs, it is most useful in investigating rail stresses due to bending moments developed in rails by the passing trains. Many attempts have been made to determine such stresses from the bending moments calculated from the known weights upon axles, and similar data, but the manner in which the roadbed reacts to the weight upon the rail is of the greatest importance in such calculations. The effects from this factor are very difficult to determine, due largely to the fact that the character of the roadbed is quite variable. Even where the material which forms adjacent portions of the roadbed is the same, nevertheless its resistance and reaction under load may vary considerably. For example, a portion of the track may be supported on solid ground and an adjacent portion on a fill. Indeed a large proportion of railway roadbed is built upon fill, which is a condition which is also favorable to the occurrence of high variations in the resistance factor or reaction under load. Another factor of importance is that of drainage, and where the drainage is not good, there would naturally be a great decrease in the reactive qualities of the roadbed. When one considers that in a single rail length great variations in the nature of its support may occur, it is obvious that under the modern practice of heavy loads, very unusual and abnormally high stresses may occur at certain localities on the roadway. It has also been attempted to determine the action of the ballast under a passing load by means of pressure capsules which are supposed to indicate the pressure developed in the ballast, but the use of such instruments necessitates the removal and replacement of the ballast and hence the test conditions are obviously not the same as those existing in the ballast before it was removed.

The general object of the present inven tion is to produce a simple process and apparatus for investigating relatively small movements of a body, and to determine maximum stresses in a loaded member. As applied to a railwaytrack, my process enables the actual distortions and stresses under the load to be accurately determined in a very simple and expeditious manner.

The invention consists in those novel steps and combination of steps, all of which contribute to produce a simple and efficient process for investigating stresses and determining the maximum stress in a structure subjected to load; and the invention also resides in the apparatus, means, diagrams or graphs which result from the use of the process. A preferred embodiment of my invention will be particularly described in the following specification while the broad scope ofmy invention will be pointed out in the appended claims.

Further objects of my invention will appear hereinafter.

In the drawing Figure 1 is a diagrammatic plan indicating how my process is practiced on a railway track;

Figure 2 is a vertical section diagrammatically illustrating the special means which I may employ to effect magnification of the rail distortions under the action of a load;

Figure 3 is a diagrammatic view illustrating the magnified variation of a portion of track from a horizontal line or axis; and

Figures 4, 5 and 6 constitute a series of diagrams or graphs corresponding to different positions of a passing load and graphically indicating the distortions corresponding to the assumed position for the load.

In practicing my process I produce a representation of the member while subjected to the load, but in this representation I magnify the distances in the direction in which the distortions of the member occur by reason of the loadg the representation is preferably simply a photograph taken with a special lens attachment which effects the magnification of all distances or measurements in the desired direction. I

If it is desired to produce a still greater magnification of the distortions the photograph may be rephotographed one or more times. Supposing that the lens produced a magnification of five times in the original photograph, it is evident that if the'original photograph were rephotographed three times a magnification of 625 times would be produced in the final photograph.

In the case of a structure that is simply subjected to a fixed load, it is merely necessary to photograph the member while subjected to the load. This would be all that would be'necessary in a member which is disposed upon an absolutely straight line when not subjected to a load. However, as few members subjected to stress are actually straight when not loaded, it isadvisable in order to produce an exact representation of the distortion, to photograph the member while it is at rest, that is to say, when not subjected to its load. This phoograph should be rephotographed in the same man,-

ner as described above, In this way two representations or photographs are produced, one of which shows the modified distortions of themember under its load and the other shows, what might be called, the magnified profile of the member. By combining these two photographs it is possible to determine exactly what the real distortion of the member is under the load.

IVhile my process may be used in this simple way to determine the stresses in a member carrying a fixed load itisparticularly useful and serviceable where the member is subjected to a live load; for example, fordetermining the stresses in track rails developed by a passing train. I shall now describe the process in detail as applied to this purpose.

In Figure 1, 1 may represent a given length of a piece of track and, for example,

we may assume that the distance between the two points 2 and 8 is fifty feet. If it is desired to investigate the stresses between these points I set up a camera, preferably a moving picture camera 4 at a sufiicient distance away from the track to take in the required fifty feet.

The camera is provided with means for focusing the light rays from the object, in

In the present instance these distortions, of course, woul d occur in a vertical'directionand the optical system is so constructed asto magnify all vertical distances. A simple lens arrangement for accomplishing this is llustrated diagrammatically inFi 2. In

this view 5 represents an 1 achromatic lens which is'mounted on a telescoping sleeve 6 so as to enable the lens to be moved in order to focus the image of the rail on the film 7 which is mounted in the camera. This film may be driven in the usual way by means of a crank 8. In the fixed barrel 9 of the camera I mount a special lens 10 which is provided with curved faces, that is to say, cylindrical concave faces 11 and 12; these faces Hand 12 are of the nature of cylinders, that is to say, the horizontal elements of the surface are parallel to a fixed or horizontal axis, but their distance from this axis varies as maybe necessary to produce the desired relative magnification. It should be noted that I use the term cylindrical in its geometric sense. In this way,aray 13 of light coming from the rail 14 would pass through the opening 15 of the stop or diaphragm 16 and after passing through the lenswould be refracted in the manner indicated in Figure 2. In this way the photograph t'akenupon the film would magnify all vertical distances and hence would. produce a magnification of any distortion or vertical movement which occurred m-the rail as the load passed over, 1t.-

With a magnifying attachment of-this nature, if a photograph were taken of a rail, or a certain length of track, the profile of the rail would be found not to be in a straight line, but an irregular line, such as the line 17 .(see Fig. 3). This line might have the relation indicated with respect'to the horizontal or straight line 18. Having taken a single photograph of the track so as to establish the magnified profile 17 of the rail, I then take a' series of pictures of the track length while the train is passing over it.

In Figures 4, 5, and 6, 19 represents a load such as a locomotive and these three figures correspond to different progressive positions of the load in passing along the track. Of course, in practice these pictures would be made at the rate of sixteen or more per second, and would, therefore, give a complete indication of practically all rail distortions I which would have occurred while the load was passing. However, Figure 4 ,merely represents the load after it has'passed about one-quarter of the length being investigated, while Figure 6 shows the load at about the last quarter of its movement. Figure 5 shows the load in mid-position.

In Figure 5 the 'line A--B represents th rail profile at the instant that the load is at the middle of the length or stretch being investigated, but, of course, with the vertical distances greatly magnified. However, it should beunderstood that this line AB would not accurately represent the distortion of the rail unless the rail was in Str ig t ondition. In order to p duce an accurate representation of the actual distortion it is necessary to combine the characteristics of the line AB with the line 17 so as to produce a resultant line C-'D. The line C-D is plotted by using ordinates such as the ordinate 3 on Figure 3. At a corresponding point on Figure 5-tl1e point 20 is found by measuring down from the line AB a distance equal to the ordinate y. In this way a diagram, graph or curveis plotted which represents the distortion in the rail profile from the normal condition of rest. WVhere there is a sharp bend in this line a relatively large fibre stress is inclicated; for example, at the bottom of this curve such a bend occurs. By drawing a tangent and a line at right angles to'it the relation of the distances indicated by the letters 0 and h on the figure can be obtained and from this data the fibre stresses may be readily computed by any of'the well known formulas. Of course, in all computations the coefficient of magnification must be used as a divisor to obtain a. correct expression of the actual stress.

It will be noted that the use of my process does not require any reference of the curve or graph to any axis. It is merely necessary to produce a representation of the rail profile under the load. According to my method it is also not necessary to compute the stresses indicated at all of the points where bends occur. This arises" from the fact that it is merely necessary to compare'the clifferent photographs with each other toascertain which photograph shows the sharpest curve in the distortion line. For example, in Figure 4:, the full line E-F represents the resultant distortion line after" combining the photograph with the normal profile line 17. This line EF may exhibit a very sharp bend at the point 21. The corresponding bend or dip in the line (1 D is indicated by the dotted line at 22 and hence it is very evident that the stress corresponding to this load position of Figure 4, developed in the rail is very much greater than that developed as indicated in Figure 5.

To further illustrate this point, the distortion line G-H shown in Figure 6' may present a sharp bend at the point 23 which might indicate a fibre stress far greater than those indicated by the other figures.

In this'way' it will be evident that by' preparing a series of these distortion graphs, diagrams or photographs corresponding to successive or progressive positions of the load'passing over the-rails, the different diagrams may be readily compared with each other by superposing them upon each other. This, of course, would be facilitated by forming the diagrams upon transparent or translucent paper. By comparing the diagrams very accurate information results as to the point of maximum stress in the rail.

It is also evident that by using the same load with different types of wheels, the influence of the different wheels on the track reaction will also be indicated by the diagram, that is to say by comparing a diagram produced with one wheel, with a diagram produced by using the same load with another wheel.

My process enables the action andreaction of the wheels on the track to be investigated in case the wheel should leave the track for an in'stai'it. In such a case the magnification of the ordinates in the photograph will indicate the position of the wheel. Knowledge of this nature mightlead to many deductions as to trackreactions at the locality photographed.

It is evident that my invention maybe used for investigating relatively small movements of a body where the movements are not cause by stresses.

It is understood that the embodiment of the invention described herein is only one of themany embodiments my invention may take, and I do not wish to be limited in the practice of my invent-ion nor in my claims,

to the particular embodiment set forth.

W hat' I claim is:

1. The process of determining the maximum stress in a member carrying a live load which consists in producing a series of representations showing a given length of the loaded member with the load in different positions, in" which the distances are magnified in the direction in which distortions occur due to the load, comparingthe representations to ascertain the point of maximum indicated distort-ion among the representations, and then computing the fibre stress corresponding to the maximum indicated distort-ion.

2. The process of determining the maximum stress in a member carrying a live load, whi'chconsists in producing a series of photographs of a given length of the member with the load in different) positions, and in which the distances represented in the photographs; are magnified in the direction in which distortions occur due to the load, comparing the photographs with each other to, ascertain which photograph and what point upon the same indicates the maximum distortion and then comput ing the fibre stresscorres aonding'" to the maximum indicated distortion.

3'. The process of dc'termining 'the maximum stress in a member carrying a live load, which consists" in producing a representation showing a given length of the unloaded member, in which the distances are magnified in a directed substantially at right angles tothe longitudinal axis of the member, producing a series of representations showing the same length of the member with the load in different positions in which the distances are likewise magnified .in a direction at right angles to the longitudinal axis of the member, producing a series of diagrams in which each diagram is the result of the combination of the first representation with one of the series of representations, so that each diagram correctly indicates the actual distortion in the memher due to the load, comparing the series of diagrams with each other to ascertain the maximum indicated distortion in the whole series, and then computing the fibre stress corresponding to the maximum indicated distortion.

4:. The process of determining the maximum stressin a member carrying a live load, which consists in producing a. photograph showing a. given length of the unload-ed member in which the distances are magnified in a direction substantially at right angles to the longitudinal axis of the member, producing a series of photographs showing the same length of the member carrying a load in; progressive different positions, in whichthe distances are like-wise magnified in a direction at right angles to the longitudinal axis of the member, producing a series of diagrams in which each diagram is the resultant of the combination of the first named photograph with one of the series of photographs so that each diagram correctly indicates the actual distortion in the member due to the load, comparing the series of diagrams with each other to ascertain the maximum indicated distortion in the whole series of diagrams, and then computing the fibre stress corresponding to the maximum indicated distortion. r

5. The process of determining the maximum rail stress in a given length of track, which consist-s in producing aseries of photographs showing a given length of the track with a load in different progressive positions passing over the track, in which the vertical distances are magnified, comparing the photographs of the series with each other to ascertain the point of maximum indicated distortion among the series, and then com puting the fibre stress corresponding to the maximum indicated distortion.

6. The process of determining the maxi mum rail stress in a given length of railway track which consists in producing a photograph showing a' given length of the track without a load on the rails, in which the vertical distances are magnified, producing a series of photographs showing the same length of track with the load in different progressive positions in which the vertical distances are likewise magnified, combining each photograph of the series with the first named photograph to produce a series of diagrams in Which each diagram correctly indicates the actual distortion in the rail due to the load, comparing the series of diagrams with each other to ascertain the maximum indicated distortionin the whole series of diagrams, and then computing the fibre stress corresponding to the maximum indicated distortion.

7. The process of investigating stresses in a. member subjected to a load which consists in producing a photograph of the member when not subjected to the load, in which distances are magnified in the direction in which distortions under the load will occur, producing a second photograph of the memher while subjected to the load, in which distances are likewise magnified in the direction in which distortions occur, and plotting a diagram which is the resultant of the two photographs, said diagram indicating the actual distortion of the member'under' the load.

8.. The process of investigating stresses in a member subjected to a load which consists in producing a series of photographs of the member in whichcdistances. parallel to an axis of selection are magnified in therdirection only in which distortions under the load occur, and ascertaining the stresses through the agency of the indicated distortions in the photograph.

9. In processes of investigating stresses photographically, the step of producing a,

subjected to the influence of an affectingforce, in whichimage distances are magnified in the direction only in which the selected movements occur which are parallel to an axes of selection, and thereupon observing such magnified movements during their occurrence.

In testimony whereof, Ihave hereuntoset In hand.

y "HARRY F. R OACH, 

